Sunday’s tally of 15,728 new cases was the lowest reported since December 28.

The seven-day average for case numbers in Australia has dropped to the lowest level since mid-February, according to Johns Hopkins data.

University of South Australia epidemiologist Adrian Esterman says while the wave of cases linked to the highly infectious BA.4 and BA.5 Omicron sub-variants appears to have reached a trough, new sub-variants continue to emerge.

“We’re seeing a wave (of infections) due to new sub-variants every three to four months, and we have done for the last eight months,” he told AAP.

“So if the same pattern continues, we might expect a new wave from a new sub-variant around November. And there’s already a couple on the horizon.”

Prof Esterman said the BA.2.75 variant was taking over as the dominant strain in India, while BA.4.6 had begun to take hold in parts of the United States.

Those strains were almost certainly already in Australia but it was too soon to know whether they would become dominant or whether a subvariant that caused more severe infections would assume their place, he said.

“There’s absolutely no guarantee that the next wave that comes along isn’t going to be incredibly severe. We simply don’t know,” he said.

States and territories have largely rolled back protections including mask mandates.

But Esterman said the persistence of the virus meant there was a need for more public health measures including greater education around mask-wearing and the importance of booster shots

“More important than the peaks of the waves is the height of the trough in between them,” he said.

“That’s staying relatively high, and that means that there’s constant pressure on our hospital systems and there’s constant pressure of people getting long Covid.”